Abstract

Some results are presented for optimum noise performance of transistor input stages when fed from resistive or reactive sources. Standard theory has shown that a common-emitter transistor fed from a resistive source presents a minimum noise figure F_m when the source resistance has a certain value R_gm in the order of lkΩ. In this
paper, expressions are developed for minimum noise figure and optimum
source resistance in the presence of base bias resistors, emitter degeneration
resistance, and various kinds of feedback. Results are in
terms of F_m and R_gm only, and do not contain other functions of the
transistor internal noise sources. It is shown that the minimum noise
figure is never less than F_m, but the optimum source resistance can be
either greater or less than R_gm.
In the case of reactive sources, noise figure is meaningless and
the quantity of interest is signal-to-noise ratio over the passband.
It is shown that for an inductive source, such as a magnetic tape head,
there is a maximum signal-to-noise ratio obtainable with an optimum
source inductance, and that a Figure of Merit can be assigned to the
source which is independent of its inductance.
Experimental results presented for both resistive and inductive
sources show good agreement with the theoretical predictions.

Item Type:

Report or Paper (Technical Report)

Additional Information:

Optimum Noise Performance of Transistor Input Circuits Presented at the Philadelphia Transistor
and Solid State Circuits Conference,
February 1958.
Published in Semiconductbr Products,
July/August, 1958.
Transistor AC and DC Amplifiers with High Input Impedance Published in Semiconductor Products,
March 1959.
Part of this material is based on work performed for Westrex Corporation,
Hollywood, California, and is reported by permission of Westrex
Corporation. The author also wishes to thank A. G. D1 Loreto and T. C.
Sorensen, of the California Institute of Technology, who performed the
experimental measurements, and the Alectra Division of Consolidated Electrodynamics
Corporation, Pasadena, California, for their kind loan of a true
rms voltmeter.
The authors wish to thank A. G. DiLoreto, T. C. Sorensen, and W. T.
McDonald, of the California Institute of Technology, for their help with
the experimental measurements. Patents covering many of the circuits
have been applied for by the California Institute of Technology.